This invention relates generally to gas turbine engines, and more specifically to methods and apparatus to reduce tip rub loads induced in rotor blades.
At least some known gas turbine engines typically include a casing, a fan rotor assembly, low and high pressure compressors, a combustor, and at least one turbine. The compressors compress air which is channeled to the combustor where it is mixed with fuel. The mixture is then ignited for generating hot combustion gases. The combustion gases are channeled to the turbine(s) which extracts energy from the combustion gases for powering the compressor(s), as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator.
Some known fan and compressor assemblies include a casing that encloses a rotor having a plurality of rotor blades. Under certain engine operating conditions, the rotor blades may be subject to blade tip rub events that induce radial and tangential loads in the blade airfoils. Excessive rub loads may facilitate damage in the blade due to vibratory and fatigue conditions. Excessive rub loads from the blade rubs may also facilitate secondary damage that includes damage to non-adjacent blades and the casing. Excessive fan blade rubs may exert large rub loads on the rotating disks and bearings if the blade plows through the fan case abradable system.
Accordingly, it would be desirable to have a rotor and casing system comprising rotor blades having features to reduce the rub loads that are induced during blade tip rubs. It is desirable to have a rotor blade having an airfoil that machines away the casing abradable material during tip rubs. It is desirable to have a method of forming rotor assemblies having reduced blade tip rub loads.